SIMULATING MICRO-FAILURE FLAWS IN FIBER COMPOSITES

A better understanding of how failure progresses until rupture in fiber composites can be gained by simulating the micro-failure modes in the specimens. When combined with highly sensitive experimental techniques like the optical Moire method, a valuable investigation tool to study the behavior of fiber composites is available. Specimens were used to simulate delamination, debonding, fiber fracture, matrix cracking, and a combination of these modes. Four specimens of each type of simulation were tested in uniaxial tension using a closed-loop servohydraulic testing machine with hydraulic grips. The average fracture stresses and the unidirectional graphite--epoxy composite specimens with delamination flaw after tensile test to failure were evaluated. Delamination failure was evident where the Teflon tape was implanted before fiber rupture and disintegration of the specimen. A quasi-isotropic graphite--epoxy laminate with a "fiber-cut" flaw was evaluated. Experimental techniques like the optical Moire method that are highly sensitive up to the micromechanics domain were used to determine the response of these flawed specimens as the load changes.